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Nanopillars on Surface of Thin-Film Silicon Could Lead to Better Solar Cells

When you start to discuss the power conversion–efficiency of solar cells, you are bound to ruffle some feathers.

To many it’s an apples-and-oranges debate. You have multijunction solar cells with conversion efficiency rates at 42 percent while dye-sensitized solar cells are now reaching just 10 percent. It's hard to see how they compare—never mind compete.

But what are we really trying to get at with this standard? It would seem that we are trying to sort out the best alternative per kilowatt hour (kWh). Why we don’t set aside the whole energy conversion efficiency debate to focus on kWh figures remains a bit of a puzzle for me.

That said, researchers at the A*STAR Institute of Microelectronics in Singapore tackled the fact that the best thin-film photovoltaics only approach half the energy conversion efficiency of conventional bulk silicon solar cells.

The research, led by Navab Singh and published in the IEEE journal Electron Device Letters, brought about a thin film of silicon with “nanopillars” on the surface to heighten light absorption.

"By investigating a variety of appropriate vertical nanopillar designs, we can enhance the light-trapping and -collection efficiency of thin films to compensate for the efficiency loss caused by reduced material quality and quantity," says Singh.

The trick, of course, is to match—or at least better approach—the energy conversion–efficiency rates of single-crystalline silicon solar cells with thin-film silicon solar cells. Whether this is the particular answer to achieving that remains to be seen, but it seems to be a move in the right direction, unlike the pursuit of ever-higher conversion rates.

Adhesion Capability of Graphene Opens New Application Possibilities

Researchers at the University of Colorado, Boulder, have discovered that graphene possesses unexpected adhesion qualities that could open it to use in new, graphene-based mechanical devices such as gas separation membranes. 

Assistant Professor Scott Bunch of the CU-Boulder mechanical engineering department, along with graduate students Steven Koenig and Narasimha Boddeti and Professor Martin Dunn, published in the August 14 edition of Nature Nanotechnology their discovery that graphene’s flexibility and its strong influence to van der Waals force make it stick to even the smoothest surfaces.

"The real excitement for me is the possibility of creating new applications that exploit the remarkable flexibility and adhesive characteristics of graphene and devising unique experiments that can teach us more about the nanoscale properties of this amazing material," Bunch said.

The experiment ran a so-called “blister test”—essentially, adhesion energy tests—on one to five layers of graphene after it had been placed on a glass substrate. The results showed that the adhesion energies between graphene and the glass substrate were several orders of magnitude higher than those found in typical micromechanical structures (0.45 ± 0.02 J m−2 for monolayer graphene and 0.31 ± 0.03 J m−2 for samples containing two to five graphene sheets).

I understand that these adhesion properties of graphene bode well for membranes for natural gas processing or water purification, and it seems a good line of research to find uses of graphene that would seemingly avoid its inherent weakness of lacking a band gap.

It will be interesting to see what other possible applications people recognize in this new adhesion quality outside of mechanical membrane technologies.

Search Terms Indicate the Expansion of Nanotechnology

Nanowerk, in its most recent Spotlight piece, has highlighted the work of two UC Davis researchers in analyzing the spread of nanotechnology research by using search terms within a scientific database that accesses over 10,000 scientific journals.

Minghua Zhang, a professor in Civil and Environmental Engineering at UC Davis, and Michael L. Grieneisen, a researcher in Zhang's AGIS Lab, have published their findings in the journal Small, in an article entitled "Nanoscience and Nanotechnology: Evolving Definitions and Growing Footprint on the Scientific Landscape."

The Nanowerk article points out that Zhang’s and Grieneisen’s work is based upon a Georgia Tech project called “Refining search terms for nanotechnology” that was published in 2008.

The UC Davis researchers added some carbon nanostructure search terms to the list—graphene, fullerene, buckyball—and excluded a few more terms from the search that may have had a “nano” prefix but weren’t really related to nanotechnology, such as “nanosatellite.” They ran the updated search terms through Web of Science Database (WoS) for the years from 1991 to 2010 and voilà.

The results showed the top five countries in terms of records were:

  • China (20 186)
  • USA (18 472)
  • Japan (6556)
  • Germany (6546)
  • South Korea (5278)

I am really only slightly surprised by these figures. Mainly, I was initially surprised that China was at the top of the list. Then I took a look back at where UC Davis researchers had done their search and where the Georgia Tech folk had decided to focus their queries.

The WoS queries I imagine spread a much wider net than Georgia Tech’s search through “key journals.”

I don’t want to malign anyone here, but I think it is altogether possible that papers published in journals outside of the top publications might rack up a lot query hits but mean little in terms of actual scientific impact.

Can Nanotechnology Improve Lithium-ion Batteries to Make a Difference for Electric Vehicles?

I have carefully followed the nanotechnology-related developments for improving Li-ion batteries for use in mobile phones and other gadgets. However, I have been less enthusiastic about the prospects of nanotechnology in improving Li-ion batteries for use in electric vehicles (EVs).

My skepticism was initially tickled by John Petersen over at Alt Energy Stocks, whom I have referred to before in this blog, and who has new ammunition in his running doubt on the future of Li-ion batteries in EVs

It seems Mr. Petersen has never been convinced that EVs powered by Li-ion batteries, nano-enabled or otherwise, were really the wave of the future. He got further confirmation of his doubts when he came across a free 2010 report from the National Research Council entitled “Hidden Costs of Energy, Unpriced Consequences of Energy Production and Use.” 

According to Petersen, the report takes a life-cycle approach to looking at the total cost of 13 different methods of powering vehicles, ranging from the internal combustion engine to Li-ion battery powered cars.

It turns out when you look at the full life cycle they’re all about the same in terms of “health, climate and other unpriced damages that arise from the use of various energy sources for electricity, transportation, and heat.” And this is not just for now but for 20 years into the future, when the technologies for things like Li-ion batteries are supposed to improve dramatically.

Petersen’s article is targeted for investors and as such discusses some of the ideas that have been investment darlings at one time or another in the Li-ion battery technology sweepstakes, such as Ener1, A123 Systems, Altair Nanotechnologies, and Valence Technologies (VLNC). He goes further to warn of dark days for the EV manufacturer Tesla:

“Lithium-ion battery developers have already taken it on the chin, and there's no question in my mind that Tesla will be the next domino to fall. Its demise is every bit as predictable and certain as Ener1's was.” 

Just so it’s clear, I am all in favor of EVs and for having them replace vehicles powered by internal combustion engines, but it just is not clear that Li-ion batteries with incremental improvements brought on by nanotechnology will be the power source for them.

Deeper Patterns and Easier Process Comes with New Etching Technique

Improved etching techniques have been making their way into the science journals of late.

Earlier this month, researchers from the University of Pittsburgh published their work in using DNA origami to both promote and inhibit the etching of SiO2 at the single-molecule level.

Now researchers at Argonne Center for Nanoscale Materials and Energy Systems Division have published two studies on a technique they have developed called sequential infiltration synthesis (SIS), which builds on long-standing lithography techniques but could be a real breakthrough in the field, according to the researchers.

The research, which was led by Seth Darling and published in two journals—Journal of Materials Chemistry and the Journal of Physical Chemistry C—involved developing a way by which to strengthen the delicate resist film to the extent that it no longer needs the intermediate mask.

What this translates into is a capability not only to circumvent all the complexities brought on by the use of an intermediate mask, but also to etch a pattern with greater depth and fidelity.

The SIS technique involves the controlled growth of inorganic materials with polymer films that can be built into complex, 3-D structures.

“It's possible we might be able to create very narrow features well over a micron deep using only a very thin, SIS-enhanced etch mask, which from our perspective would be a breakthrough capability," says Darling.

The researchers are looking at expanding the capabilities of the technique by combining SIS with block polymers to make features even smaller than those possible with e-beam lithography.

"This opens a wide range of possibilities," said Argonne chemist Jeff Elam, who helped create the process. "You can imagine applications for solar cells, electronics, filters, catalysts—all sorts of different devices that require nanostructures, but also the functionality of inorganic materials."

Quantum Dot-Based Infrared Materials Gets DARPA Contract

Massachusetts-based QD Vision announced this week that it had been awarded a $900,000 DARPA contract to build two prototype devices based on its quantum dot-based infrared material.

According to published reports, QD Vision “will deliver to DARPA a device with quantum dots as an emissive layer in an electroluminescent electronic device application, and a second, photoluminescent device that is based on a film that is activated by external light sources.”

"This program will leverage QD Vision's experience in developing stable, efficient IR materials for tactical applications," said Jason Carlson, President and CEO of QD Vision. "This is our second DARPA Program as a prime contractor, and we are excited to demonstrate these novel materials in two distinct modes of operation."

This most recent contract follows a US $22 million funding round received just this past May. So, for the company to get a nearly $1 million DARPA contract in just three months must have caused a sigh of relief in the investors.

To get a great backgrounder on the development of quantum dots for application in infrared detectors I refer you to this article written last year by Edward Sargent here on the pages of Spectrum.

In the article, Sargent points out just how quickly infrared detectors based on quantum dots are developing into commercial devices:

"Much closer to commercial development are quantum dots that are exquisitely sensitive to faint infrared light. With only a few years of research behind them, these devices now perform as well as the best traditional infrared detectors."

It appears that commercial development might have been closer than Sargent had even imagined. Granted, it's only a contract for defense department prototypes, but it's a sale nonetheless.

Nanotechnology's Role in the Lithium-ion Battery Anode and Cathode

A recent story in Spectrum covers the commercially promising work being done in using silicon to replace graphite in the anodes of Li-ion batteries.

These developments do hold promise for introduction of these new batteries into our personal electronic devices relatively soon. I have been so intrigued by this line of research I have been highlighting it for nearly four years

One of the key points of the recent Spectrum article referenced above is a discussion of a timeline for these nano-enabled batteries that ranges from two years out to early next year.

Timelines for this sort of thing are a tricky business. I wrote earlier this year on how Nanosys had developed a “silicon-based, architected material that fills in the voids of the carbon anode material matrix” that “remains intact and fully functional after 100% DoD cycle testing.” It also “demonstrated a >2× capacity improvement using 10% additive in a Li+ battery anode.”

When this material was announced, Nanosys was expecting volume sales of the material this year—in 2011. I went to the Nanosys Web site to see how this timeline was progressing, and I saw this: “Nanosys is working in collaboration with the world’s leading lithium-ion battery manufacturers to deliver unprecedented energy performance in new products coming to market over the next 18 months.”

I would imagine that it could be on the far side of two years from now before we see Li-ion batteries that have silicon on their anodes in our gadgets. But we’ll see.

The Spectrum article also suggested that now that the anode side of the battery seems to be covered, work is now turning to improving the cathode. Indeed it has. I bring your attention to the work of researchers at the University of Urbana-Champaign in building 3-D nanostructured cathodes. 

Nanotech Terrorists Apparently Don't Know What Nanotechnology Is

The confusion—which now seems insurmountable—over the advanced material science that accounts for the nanotechnology being used in products today and the molecular mechanosynthesis of the famed “nanobot” variety has now resulted in violence.

Some radical group that calls itself “Individuals Tending Toward the Savage” (oh dear!) has taken credit for at least two bomb attacks on Mexican researchers and written up a manifesto to accompany the attacks that expresses “fears that that nanoparticles could reproduce uncontrollably and form a 'gray goo' that would snuff out life on Earth.”

I have done my bit with the baby-talk explanation that would prevent people from confusing nanoparticles with mythical “gray goo,” but sometimes stupidity is just too difficult to overcome.

I first heard about threats to nanotechnology research facilities when attending the opening of IBM’s new nanotech lab in Zurich back in May. I have since learned that three so-called “eco terrorists” were convicted of planning to bomb the IBM facility

It seems to me there might be much to be radical about in this day and age, but focusing your frustration and outrage at a bunch of material scientists who ride their bikes to work and spend their days focusing atomic force microscopes hardly seems like it’s well directed or helpful.

It’s even worse when you clearly have no idea of what you’re talking about. You need to know what nanotechnology is before you can be outraged by it. 

The Unfulfilled Quest for a Good Nanotech Investment Article

My initial reaction to a new article on nanotechnology investment advice is typically less than welcoming. But today there were a couple of reasons for me to take an interest, such as the recent news that early-stage VC investors make a 2.4% higher return than their later-stage counterparts.

This kind of data might encourage investors to start early on the long road of investing in a company trying to make its way to profit with a nano-enabled product. It might also help the US economy get out of its liquidity trap.  (One can always hope.) And, if so, a little good investment advice in nanotech could be useful, especially given the discouraging news we seem to get on a regular basis on nanotech-start-up companies.

So, I decided I was going to read the latest article in this vein with as much open-mindedness as I could possibly muster.

The article entitled “Should Investors Roll the Dice with Nanotechnology?” is authored by Deborah Sweeney, the CEO of MyCorporation.com. I am sorry to say I had never heard of Ms. Sweeney before, but it seems she comes at this issue from a background in legal services.

Fair enough. It’s not exactly a background one would associate with having extensive knowledge on how to invest in an emerging technology, but you never know who might have something interesting to say.

Unfortunately, I can’t report that there is anything interesting here as it’s burdened with well-worn platitudes like, “Great rewards typically only come with great risks…” or “Before looking at a project, and potentially sinking money into it, investors must ask if this can be sold to someone.”

Really? You think? While giving a test run of every investment cliché, not one mention is made of investment horizons and how this factors into investors’ formula for risk, or how much better a nanotech-enabled product needs to be over its competitors to take a portion of the market, and how the funding gap between government research projects to commercial products is supposed to be bridged when the private investment community is keen to wait on the sideline until profits are made. 

And who are the investors this article is supposed to be addressing—VCs, stock traders, private equity? It's hard to imagine any of them sitting down to read this to inform their investments.

The question of funding and investment to further the commercialization of nanotechnology is fundamental and critical. It really deserves to be addressed better than this. 

I held my nose and took a bite, and now that I’ve swallowed it, I feel a little ill and have a bad taste left in my mouth. It might be a while before I try this again.

Paradigm Shift in Understanding of Biology Could Alter Electronics

The discovery that microbial nanowires inside the bacterium Geobacter sufurreducens can conduct electricity not only represents a paradigm shift in our fundamental understanding of biology but also could completely change how we manufacture and use electronics.

Researchers at the University of Massachusetts, led by microbiologist Derek Lovley with physicists Mark Tuominen and Nikhil Malvankar, have discovered that the Geobacter bacterium uses the nanowire-like protein filaments to transfer electrons into iron oxide (rust) contained within the soil where they live, and that this mechanism serves the same function as oxygen does for humans.

While the research, which was published in the August 7th advanced online edition of Nature Nanotechnologyrepresents the first time that metallic-like conduction of electrical charge has been observed in a protein filament, the researchers had conjectured as far back as 2005 that this was the case.

Because they didn’t have the mechanism to demonstrate this capability, their hypothesis was met with a fair amount of skepticism. It was believed that if such conduction occurred, it had to involve a mechanism that used a series of proteins known as cytochromes.

The researchers were able to continue their research in a fairly simple way by allowing the Geobacter to grow on electrodes, where the bacteria produce a electrically conductive biofilms. The researchers were able to use a series of genetically modified strains of the bacterium to narrow down the source of the metallic-like electrical conductivity inside the biofilm to a network of nanowires within the bacterium.

"This discovery not only puts forward an important new principle in biology but in materials science,” says Mark Tuominen in the U Mass press release. “We can now investigate a range of new conducting nanomaterials that are living, naturally occurring, nontoxic, easier to produce and less costly than man-made. They may even allow us to use electronics in water and moist environments. It opens exciting opportunities for biological and energy applications that were not possible before."

While Lovley (the microbiologist) has been working with the Geobacter bacterium now for nearly two decades in everything from bioremediation to the synthesis of biofuels (see video below), it was the addition of the physicists to the research that could make this a significant breakthrough in electronic materials research.

 

“As someone who studies materials, I see the nanowires in this biofilm as a new material, one that just happens to be made by nature, says Tuominen. “It’s exciting that it might bridge the gap between solid-state electronics and biological systems. It is biocompatible in a way we haven’t seen before."

While mobile phones that you can use while scuba diving may be a long way off, this would seem to be an inexpensive way to replace nanowires made from toxic and expensive materials in everything from biosensors to solid-state electronics that are used in connection with biological systems.

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Nanoclast

IEEE Spectrum’s nanotechnology blog, featuring news and analysis about the development, applications, and future of science and technology at the nanoscale.

 
Editor
Dexter Johnson
Madrid, Spain
 
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Rachel Courtland
Associate Editor, IEEE Spectrum
New York, NY
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